Hyperhomocysteinemia is a common metabolic disorder that causes a significant increase in the total level of plasma homocysteine. In spite of the FDA-mandated fortification of food with folic acid, as an attempt to lower homocysteine levels, the incidence of hyperhomocysteinemia in the elderly population is still quite large. This is mainly due to lowered nutritional absorption and decreased metabolic function with advanced age. Emerging evidence suggest that pre-disposition to hyperhomocysteinemic conditions may be associated with aggravation and acceleration of neuronal injury and subsequent brain damage in individuals suffering from Alzheimer's and Parkinson's diseases or acute ischemic stroke. However the pathological implications or the molecular basis of neurological insult in individuals predisposed to hyperhomocysteinemia is yet unknown. Our findings now show that a mild ischemic insult in hyperhomocysteinemic animals exacerbates brain injury. The findings also show that homocysteine-dependent neurotoxicity involves a novel-signaling pathway that is mediated through NR2A- NMDA receptor stimulation. The long-term goal of our research is to develop therapeutic interventions for reducing the adverse effect of hyperhomocysteinemia on cerebral ischemia and related neurodegenerative disorders. The objectives of this particular application are to examine the molecular basis of homocysteine induced neuronal injury and evaluate the long-term progression of ischemic brain damage and neurological deficits in hyperhomocysteinemic animals. The central hypothesis is that homocysteine-NR2A-NMDA receptor signaling triggers a deleterious signaling cascade that acts in concert with ischemia-induced pathways to exacerbate brain injury. The proposed studies will use (1) primary neuronal cultures to delineate the deleterious signaling cascades that are activated following homocysteine-dependent NR2A-NMDA receptor stimulation; and (2) Magnetic resonance imaging (MRI) and a battery of behavioral tests for longitudinal evaluation of ischemic brain injury and neurological outcome in hyperhomocysteinemic animals. The study will further evaluate whether disruption of NR2A-NMDA receptor dependent signaling could minimize brain damage associated with stroke under hyperhomocysteinemic conditions. The proposed research is significant since it will provide the first direct evidence for the role of hyperhomocysteinemia in the progression of ischemic brain injury. Understanding the underlying mechanism(s) of homocysteine induced neuronal injury will facilitate the development of potential targets to attenuate the detrimental effects of hyperhomocysteinemia in cerebral ischemia and other age-related neurodegenerative disorders.